The present invention relates, in general, to the field of laser rangefinding and speed measurement instruments. More particularly, the present invention relates to a laser sensor module array for vehicle identification, speed monitoring and traffic safety applications.
Police have been using radar and laser speed measurement devices to determine vehicle speed in traffic enforcement operations for many years now. With respect to radar based devices, they generally function such that a microwave signal is emitted toward a moving vehicle and a reflection from the target returned to the device which then uses the determined Doppler shift in the return signal to determine the vehicle's speed. Radar based devices have an advantage over handheld laser based devices in that they emit a very broad signal cone of energy and do not therefore, require precise aiming at the target vehicle. As such, they are well suited for fixed and mobile applications while requiring little, if any, manual operator aiming of the device.
On the other hand, laser based devices employ the emission of a series of short pulses comprising a very narrow beam of monochromatic laser energy and then measure the flight time of the pulses from the device to the target vehicle and back. These laser pulses travel at the speed of light which is on the order of 984,000,00 ft/sec. or approximately 30 cm/nsec. Laser based devices then very accurately determine the time from when a particular pulse was emitted until the reflection of that pulse is returned from the target vehicle and divide it by two to determine the distance to the vehicle. By emitting a series of pulses and determining the change in distance between samples, the speed of the vehicle can be determined very quickly and with great accuracy.
U.S. Pat. No. 6,965,438 describes a vehicle measuring system incorporating a number of laser distance sensors mounted in a fixed, linear arrangement over a roadway to enable the height and width of vehicles passing thereunder to be determined, for example, in a toll collection system. The system described requires an overhead structure spanning all lanes of a roadway rendering it undesirable for multilane applications while concomitantly necessitating the provision of a large number of laser distance sensors in order to accurately assess the varying height and width dimensions of all vehicles passing under the system. Still further, the vehicle measuring system described does not contemplate or disclose the determination of vehicle speed.
Laser Technology, Inc., assignee of the present invention, designs, manufactures and sells laser based traffic sensors such as the TruSense™ T100 and T200 devices. In a particular implementation of a speed system incorporating these sensors, two sensors may be utilized in conjunction with a spacer bar in which the devices are separated by approximately 80 cm longitudinally adjacent a roadway. With appropriate processing circuitry, a vehicle's presence triggering a first of the two sensors initiates a timer, which followed by the vehicle's triggering of the second sensor, enables the speed of the vehicle to be determined with a resolution of 1 mph. Such a system can also be utilized to count, profile and classify vehicles, determine the separation between vehicles as well as calculating their speed.